Briquette for lowering the viscosity of metallurgical slag and process for its production

ABSTRACT

Briquettes for the liquefaction of metallurgical slag are formed from a mixture containing, by weight, 85-98% slag from secondary aluminium processing, 1 to 8% polyvinyl acetate dispersion as the polymeric bonding agent and the remainder water, the briquettes containing water in the form of residue humidity at a quantity of maximally 1.5%, ideally no more than 0.5%, in relation to the overall weight of the briquettes, and the briquettes have a specific weight of 1,500-5,000 kg.m −3  and a compression strength of at least 20 MPa. Ideally, the mixture contains 90-92% slag from secondary aluminium processing, 1 to 3% polyvinyl acetate dispersion and the remainder water. The mixture may also contain 0.5-2% unsaturated acid, selected from the group containing oleic acid and/or palmitic acid and/or stearic acid, as a hydrophobic ingredient. The ideal shape of the briquettes is cylindrical.

TECHNICAL FIELD

The invention concerns briquettes for the liquefaction of metallurgicalslag, composed of a mixture consisting of slag from secondary aluminiumprocessing as the basic ingredient, plus a polymeric bonding agent andwater. The invention also concerns a method for production of suchbriquettes.

BACKGROUND ART

During the manufacture of aluminium, various kinds of slag are createdcontaining different quantities of accompanying elements and compounds.At the present time, slag from secondary aluminium processingconstitutes a waste product in the manufacture of aluminium and occupiesa large amount of utility space in the form of heaps. In addition, whenthis slag is stored in heaps, it decomposes under the influence ofatmospheric conditions and releases foul-smelling and harmful ammonia,causing significant deterioration of the environment. During the processof dumping, this slag gradually acquires a fine grainy consistency, thusgenerating a quantity of mineral and aluminate dust.

Slag from aluminium production is further processed by crushing andwashing out, so that the residue aluminium may be obtained. Theremaining part, which consists of a mixture of oxides, chlorides,fluorides and metal particles, particularly on a base of Al, Na, K andSi, is mostly dumped out or is very difficult to use.

Much of the technology that has already been introduced is applied tothe use of the metallic parts of scum, or these scums and slags arewashed out with water after granulometric treatment by crushing andmilling. The first method generates a segment of waste that cannot beprocessed, i.e., the already mentioned mixture of metal particles andoxides.

In other cases where these waste products are extractible etc. aftermilling, a large quantity of gases are produced, including ammonia,acetylene, methane, sometimes arsines, phosphines, in addition to saltsolutions and sludge. A drawback of these manufacturing processes is thecreation of dangerous gases, salt solutions and sludge, whoseliquidation requires large quantities of energy or complicatedapparatus.

For example, in the Czech published patent application PV 830-95, amethod is described for processing the dust fractions of aluminium scum;according to this method, the scum and aluminium waste are leached,without any kind of treatment, and dissolved in an air-excludingenvironment in a leaching solution containing chloride ions; in thisenvironment, the carbides and nitrides decompose and the aluminiumreacts. The resultant ammoniac, hydrogen, methane, appropriately thephosphines, arsines and other products are burned at a temperature of800-1,000° C. The remaining pulp is filtered off. A mixture of chloridesalts is crystallised out from the water solution under heat. The filtercake is dried and without the presence of carbides, carbonitrides, metalaluminium etc. is granulated into pellets or briquettes.

The disadvantage of this method is the complicated machinery,manufactured mainly from rust-free material or material otherwiseprotected against corrosion, with problems in the capture of thereleased gases for hygienic and environmental reasons. This relativelycomplicated method is demanding in terms of energy consumption and isrelatively costly in terms of investment and manufacture.

A certain improvement is seen in the complex agent described in theCzech published patent application PV 2914-90, which is designed for theliquefaction of slag with desulphurising effects. Here, in the finingprocess of steel-making, cryolite deposits created as waste substancesduring the electrolytic manufacture of primary aluminium are used asdiluting agents for slag. The complex agent may be used in crushed statewithout further treatment or the addition of other components. Theinvention does not solve the problem of using the waste from themanufacture of secondary aluminium, in which it is usually necessary tosecure the consolidation of the powder and fine-grain components of theslag from this manufacturing process.

In metallurgy, during the melting of iron and steel to reduce viscosityand facilitate the removal of slag during melting, fluorite, alow-profile and relatively expensive substance, is used as one of thecomponents for liquefying the slag.

Slag from secondary aluminium processing, which up to now has beentreated as manufactural waste, could be a valuable substitute forfluorite. Slag from secondary aluminium processing cannot be used inferrous metallurgy as a liquefying agent in its original loose or powderform, as handling is inconvenient and makes the work-place very dusty ina manner contrary to industrial safety regulations.

Therefore, when slag from secondary aluminium processing is used inferrous and steel metallurgy, it is suitable to process it intobriquette form, enabling the ecological improvement of the environmentand the work-place.

The manufacture of briquettes from slag makes use of various types ofbonding agents, such as water glass, lime milk, molasses and other typesof suitable adhesive substances. These substances, however, do notensure a sufficient degree of strength in the briquettes.

Austrian patent AT 390 965 describes technology for the processing ofaluminium scum, i.e. coarse-grain dross which are crushed. Metalaluminium is thus obtained, and the solid residue is further Itprocessed into briquettes for the liquefaction of metallurgical slag. Asthe bonding agent, complex polymers with large amounts of radicals areused, such as the methyl group CH₃, the ammonium group NH₄, the phenylgroups, the cyanide groups CN and metal traces. These polymers aremanufactured by means of complicated technology. In addition, at hightemperatures they decompose and release poisonous substances such asphenol and hydrogen cyanide. Very high temperatures, ranging from 1,800to 2,800° F. (900-1,540° C.) are used to polymerise the mixtures.Heating to such temperatures makes the technical process ofpolymerisation expensive and complicated. The granulation technologymentioned above is not suitable for slag from secondary aluminiumprocessing, as its large reactive capacity causes a decomposing reactionto take place in the granules, which in turn causes the granules to losetheir strength and resistance to decomposition. The highest strengthvalue for the dry granules thus obtained is 21.9 psi, corresponding to0.16 MPa, which is not sufficient for briquettes from aluminium slag.The highest strength value is obtained by the addition of clay to themixture. But the addition of clay for the purpose of binding theparticles of aluminium slag also seems to be unsuitable, owing to theconsiderable increase in the quantity of SiO₂ in the mixture and to thehigh firing temperature of 2,800° F. (1,540° C). Reducing the quantityof clay leads to rapid reduction in the strength of the briquettes downto 0.016-0.02 MPa. For these reasons it is clear that the composition ofbonding agent and manufacture of granules is not very suitable for theprocessing of slag from secondary aluminium processing into briquettes.

The purpose of this technical discovery is to obtain a cheap liquefyingagent from slag from secondary aluminium processing that has identicalproperties to fluorite in the liquefaction of metallurgical slag, insuch a manner or with such equipment as to minimise the disadvantagesoutlined above.

SUMMARY OF THE INVENTION

This aim will be achieved with briquettes for the liquefaction ofmetallurgical slag composed of a mixture of slag from secondaryaluminium processing, as the basic component, a polymeric bonding agentand water, in accordance with this invention. The substance of thisinvention lies in the fact that the mixture contains, by weight, 85-98%by weight slag from secondary aluminium processing, 1-8% by weightpolyvinyl acetate dispersion as the polymeric bonding agent, and theremainder water; and that the briquette contains water as residuehumidity at a quantity of up to 1.5% by weight, ideally to 0.5% byweight, as related to the total weight of the briquette, where thebriquette has a specific weight ranging from 1,500-5,000 kg.m⁻³ and astrength under pressure of at least 20 MPa.

The ideal content of the mixture is, by weight 90-92% slag fromsecondary aluminium processing, 1-3% polyvinyl acetate dispersion andthe remainder water.

It is also beneficial when the mixture also contains 0.5-2% by weightunsaturated acid selected from the group that includes oleic acid and/orpalmitic acid and/or stearic acid as a hydrophobic ingredient.

In its advantageous version, the briquette has a cylindrical shape.

The briquette according to this invention is obtained by the method ofmanufacture according to this invention, the essence of which is thatthe various components of the mixture, i.e. slag from secondaryaluminium processing, polyvinyl acetate dispersion as bonding agent,water, with the possible addition of a hydrophobic ingredient, areblended into a homogenous state in a mixer in a time of 10-60 seconds.The homogenous mixture thus obtained is then pressed at a specific presspower of 110 to 130 MPa. The briquette is then dried at a temperature of120 to 200° C. for 30-60 minutes, depending on the weight of thebriquette, until residue water in the briquette reaches a value of 1.5%at maximum. After drying, the hot briquette is cooled. The cooledbriquette is wrapped for protection against humidification until furtheruse or processing.

For the blending of the components into a homogenous state in the mixer,it is useful if the mixture is preheated to a temperature between 25 and99° C.

After drying and before wrapping, it is essential to cool the hotbriquette to a temperature between 30 and 50° C.

The main advantage of this invention is that slag can be used as aliquefying agent in metallurgy, e.g. in the manufacture of iron andsteel to lower the viscosity of the melt, which considerably reducescosts. Thus a waste product generated by the manufacture of aluminium isutilised, as this waste product stored in heaps decomposes under theinfluence of various climactic conditions, simultaneously giving offfoul-smelling or harmful substances such as ammonia, methane, hydrogenand phosphines. This represents another benefit of the invention, namelythe improvement of the environment, including the working environment,and the release of utility areas previously used for slag heaps. Thus itis possible to process the portion of scum that is difficult to processinto an environmentally friendly product.

In order to obtain briquettes with sufficient strength under a pressureof at least 20 MPa, it is proposed that the composition of briquettesinclude a polymeric bonding agent, namely polyvinyl acetate. Briquettesfor the liquefaction of metallurgical slag may have varying degrees ofstrength and stability during storage, depending on the choice ofpolymeric substance and its composition. Briquettes of cylindrical shapeweighing 50 to 250 g have the greatest strength. To guarantee equaldistribution of the bonding particles of the polymeric substance betweenthe particles of slag, the briquettes contain water.

According to its physical properties, slag is a consolidated substance.The specific weight of slag before processing into briquette form isapprox. 1,100 kg.m⁻³. In order to obtain briquettes of sufficientstrength, it is essential that their specific weight amount to between1,500 and 5,000 kg.m⁻³.

The proposed invention uses polyvinyl acetate, a very simple polymerthat is cheap to manufacture:

The polymer has one radical, namely the acetate group OCOCH₃.

When this polymer decomposes, it releases substances that are notharmful to living organisms. These substances include water, carbondioxide and acetic acid. In essence it is a polymeric, coarselydisperse, non-plasticized, viscous liquid, slightly yellow white incolour, with particles 1-3 micrometers in sized, devoid of granules oralien mechanical intrusions. The weight proportion of dry residue is atleast 51%. The weight proportion of remanent monomer is up to 0.5%. Theusual viscosity, according to the standardised measuring-vesselmeasurement, is 11-40, expressed as a Saybolt number. Adhesive power isat least 450 N/.m⁻¹.

So that the briquettes according to this invention may be used for theliquefaction of metallurgical slag, they must have not only sufficientstrength and stability in storage, but also a minimal cost. If thequantity of the polymeric ingredient in the composition of thebriquettes is increased, the briquettes' strength and resistance tdecomposition is increased, but the cost of manufacture rises sharply to10-20 times the amount. For this reason, to preserve a minimal cost ofmanufacture whilst obtaining the necessary strength and resistance ofthe briquettes, the polymeric substance may be partly replaced byhydrophobic ingredients. The addition of at least one hydrophobicingredient to the mixture for briquette manufacture, in a quantity of0.5-2% by weight, acts in a water-resistant way and significantlyreduces the absorption capacity of the briquette whilst considerablylengthening the storage period. For the hydrophobic ingredient,unsaturated acids such as palmitic acid, stearic acid and oleic acid areused. The acid used most often is oleic acid, described by the chemicalformula C₁₇ H₃₃ COOH, which exists in two crystalline modifications,alpha and beta, with melting temperatures of 13.4 and 16.3° C.respectively. At room temperature this acid has a specific weight of0.089 g.cm⁻³. Both of these acids may be used as pure chemicals or inmixtures of 0 to 100% in mutual combination. These acids reduce thehydroscopic properties of the mixture and the subsequent absorption ofatmospheric humidity. They may also be used as lubricants in pressingmachines.

For an equal distribution of the bonding particles of the polymericsubstances and the hydrophobic ingredient among the particles of slag,as well as for the reduction of the internal and external abrasiveforces arising as a consequence of pressing, water is added to thebriquettes. The water may be either service water or tap water.

So that the briquettes from secondary aluminium processing may be usedfor the liquefaction of metallurgical slag, they must have sufficientstrength and resistance to decomposition. The manufacture of briquettesfrom secondary aluminium processing using ordinary humidifyingtechnology is not feasible, as the briquettes thus obtained decompose in20-40 minutes while drying in the air. This occurs because some of thecomponents of the slag, e.g. the aluminium nitrides Al_(x)N_(y) and Alaluminium, enter into a chemical reaction with the water, generating,heat and gases such as ammonia and hydrogen. The gases thus releaseddisrupt the bonding between the particles and the briquettesdisintegrate.

The components of the briquette mixture are mixed into a homogenousstate in a mixer in a time of 10-60 seconds. The mixing time of 10seconds is the minimum time necessary for the mixture to be fullymoistened, whilst 60 seconds is the maximum mixing time in order toavoid speeding up the heightened decomposition of the slag. At first,the bonding ingredients and the water are mixed in a special mixer ofe.g. circular type. In this type of mixer, the polymeric dispersion issubsequently mixed with the slag from secondary aluminium processing.The mixture is deemed homogenous when the homogenised briquette mixturecompresses slightly and its component ingredients do not separate.

The pressing of the briquettes is carried out at a specific press powerof 110 to 130 MPa, which guarantees the compression strength of thebriquettes and ensures that the bonding agent and any hydrophobicingredient is squeezed out to the surface of the slag grains.

To dry the briquettes, a temperature of 120-200° C. is recommended, fora time of 30-60 minutes depending on the weight of the briquette, sothat the water necessary for soaking the surface of the slag can beremoved in order to avoid unwanted decomposition of the slag. Thus thetemperatures for polymerising and drying the briquettes are sufficientlylow, reducing the cost of the processing. Drying can be done in a dryingapparatus of rotational type.

After drying, the hot briquettes are usually easily cooled. If this doesnot take place, there is a risk that they will re-absorb humidity anddisintegrate. The briquettes can be artificially cooled to 30-50° C.,according to the type of packaging used thereafter. Cooling may becarried out naturally or artificially in a cooling conveyer.

The cooled briquettes are wrapped up for protection against humidity by,for example, atmospheric precipitation and excess humidity, untilfurther use or processing.

The proposed method allows part of the scums that are difficult toprocess to be processed into a product which is acceptable with regardto protection of the environment and which saves primary raw materialresources, especially fluorite, quartz sands, aluminium oxide orbauxite.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described below in detail in a variety of possibleversions. The technological process of briquette manufacture isschematically depicted in concise form in the appended figure.

DETAILED DESCRIPTION OF EMBODIMENT EXAMPLES EXAMPLE 1

The slag, obtained from secondary aluminium processing and destined forbriquetting, has the following chemical composition converted to knownsubstances at weight percentage:

60-65% Al₂O₃

8-10% SiO₂

5-10% Al (OH)₃

7-10% MgO

5-7% NaCl+KCl

up to 3% Na₃AlF₆

up to 1.5% ZnO

up to 1.5% CaO

up to 1.5% Al_(x)N_(y)

up to 1.5% Fe

up to 1.5%Cu

traces up to 25% Al

traces: P, As, C, Ni, V, Cr, Mo, Ti.

In mineral terms, slag is an aluminosilicate.

The module of Ma activity fluctuates around the 6.5 mark.

Basicity is usually 0.17.

Slag is acidic, and decomposes of its own accord during storage. Itcontains hygroscopic components such as nitrides, carbides and reactingaluminium, which absorb humidity from the surroundings. Components suchas aluminium nitrides Al_(x)N_(y) and aluminium Al decompose oninteraction with water and release a large quantity of heat and gasessuch as ammonia and hydrogen:

AlN+3H₂O=Al(OH)₃+NH₃

2Al+6H₂O=2Al(OH)₃+3H₂

Under the influence of the gases released, the slag decomposes intosmall particles sized 0.1 to 1.5 mm. These dimensions are entirelysuited to the granularity requirements of the charge in briquettemanufacture, and assist the operation of crushing the slag. In briquettemanufacture, the slag is loaded into the mixer either directly from theslag heaps in its natural state, or from the crushing apparatus. Powderand individual larger particles measuring 4 to 6 mm are admissible asinclusions.

Before the polyvinyl acetate dispersion is added to the slag, it ispreliminarily dissolved in water. The presence of water is essential forthe equal distribution of the particles of polyvinyl acetate dispersionamongst the particles of slag, as well as for the reduction of theinternal and external abrasive forces arising in consequence to thepressing of the slag. It is necessary to use water here only in acertain amount, as any excess water is pressed out through the edges ofthe pressing apparatus during pressing, thus leading to technicalproblems, damage to the machinery and pollution of the work-place. Onthe other hand, an insufficient quantity of water leads to unequaldistribution of the particles of polymeric bonding agent, which has anegative effect on the properties of the briquettes manufactured. Wateris actually harmful to the briquettes, and the water content in theexample versions has been set at the optimum level for the particularslag. In fact, the water content covers the fluctuating composition ofthe slag, particularly with regard to metal aluminium nitrides,carbonitrides and any other compounds.

Briquettes for the liquefaction of metallurgical slag according to thistechnical method are manufactured as follows:

Firstly, the polyvinyl acetate is mixed with water in a separate mixer,and the polyvinyl acetate dispersion thus obtained is fed, in a certainquantity, into another mixer, where it is mixed carefully with the slagand hydrophobic ingredient. After mixing, the briquetting mixture thusobtained is fed into a press, where the briquettes are pressed at aspecific press power of 110 to 130 MPa, ideally at 125 MPa. Afterpressing, the briquettes are transferred to a drying apparatus ofcircular type with a cooling conveyer. After cooling, the briquettes arewrapped in a material such as polyethylene.

As far as dosing is concerned, there is a dosing system with continuouscyclical operation, which is used in concrete manufacture. In themanufacture of slags mixtures, it is necessary that the dosing ofindividual components be precise, and thus volume dosers are suitablefor this technology. The manufacture of slag mixture is accompanied bythe release of aluminium powder, which has an adverse effect on theworking environment, so that it is convenient to exclude the presence ofa person controlling the mixing process. For this purpose, it makessense to use automatic systems for controlling the loading, dosing andunloading of materials in cyclical dosers. Automatic weight dosers withindirect action according to the construction principle of the automaticregulation system are divided into dosers with direct and dosers withindirect effect. Direct-effect dosers have in one unit an apparatus forweighing and measuring material. Indirect-effect dosers have twoseparate units, one for weighing and the other for measuring. Weightdosers consist of the following basic parts: a weight dosing tank,loading apparatus, weighing apparatus for receiving the load, a weighingmechanism and control mechanism. The loading apparatus may be arrangedas a valve whereby the flow of material supplied to the doser from thetank is admitted and regulated. In the manufacture of the slag mixture,a special doser for dosing slag and for the dosing of liquid may beused. Automatic dosers for liquids may be bifractional and may enablethe weighing of two components: water and the polymeric ingredient.Automatic dosers for slag may be monofractional or bifractional. Thesetypes of automatic dosers may have various modifications allowing themto be used for production lines of varying degrees of performance. Toensure the operation of dosers in automatic regime there are digitalindicators furnished with devices for setting the doses and forremote-controlled data transfer and automatic control.

As far as the mixing apparatus is concerned, during the process ofmixing the slag with the polymer substance, as has already been said, itis essential that the quantity of water in the slag mixture is minimal,and it is necessary to make sure that the mixing of the slag with thepolymeric ingredient is done homogenously. Thus a mixer which carriesout the mixing process as productively as possible must ensurehomogenous mixing of all the ingredients in a short period of time, mustachieve high productivity and must have a mixing bowl of sufficientcapacity. During the course of research, it was discovered that, out ofall the types of mixer, the type that most fits these requirements isthe rotational and turbulent type cyclical blender of concrete mixtureswith forced mixing of components. The technical properties of thesemixers fluctuate within the following margins: mixing time 10-60seconds, performance 2.6-32 m³.h⁻¹. These technical properties enablethese mixers to be used for production lines of varying degrees ofperformance.

A slag briquetting mixture that is ready for briquetting and has therequired composition is obtained with the precise dosing of individualcomponents, i.e. slag, water and additives, prior to their feeding intothe slag mixer. Inaccuracy in the dosing of individual components of theslag mixture is admissible to a degree of ±2% for water and additives,and ±3% for slag, by weight.

After mixing in the mixer, the slag mixture proceeds to the pressmaschine, which carries out the briquetting process.

The above-mentioned slag is, according to its physical properties, aconsolidated substance. For the briquettes to acquire sufficientstrength, it is necessary that their specific weight be at least 1,500kg.m⁻³, and in certain cases up to 5,000 kg.m⁻³. A specific weight suchas this is obtained by means of a press power equal to approx. 110 to130 MPa, with an optimum of about 125 MPa, which allows alow-performance pressing apparatus to be used. If the manufacturingprocess requires high performance, then it is possible to use pressingby the plate holder method, on presses with a high specific press power.To increase the performance of the lines, it is inevitable to useautomatic presses enabling automatic loading and unloading of the press.

The briquette-drying process is also important, and plays a decisiverole in the manufacture of briquettes from slag from secondary aluminiumprocessing.

It has already been stated that water, which is necessary for thebriquetting process, in the end has a negative effect on the strengthand resistance of the briquettes. During the course of 25-40 minutesafter pressing, a chemical reaction takes place in the briquettes owingto the presence of Al_(x)N_(y) and H₂O, after which the briquette losesits strength and disintegrates. Up to now, this reason contributed tothe fact that slag from secondary aluminium processing could not be usedin ferrous and steel metallurgy without treatment. The addition of apolymeric ingredient not only bonds together the particles of slag, butalso considerably reduces the speed of the reaction, although it cannotcompletely halt its progress. Thus it is necessary to subject thebriquettes to drying immediately after pressing. Any heating unit may beused as the drying apparatus, provided that the heat in the operatingchamber may be raised to 200° C. The drying process must continue untilminimal humidity is attained in the briquettes, which, at a temperatureof 120-200° C., takes 30-60 minutes, depending on the weight of thebriquettes.

As experiments have shown, the shape and size of the briquettes have acertain influence on their strength and length of life. The strongestand most resistant briquettes are smallish briquettes of cylindricalshape, weighing between 50 and 250 g, with advantage about 120 g.

Slag from secondary aluminium processing is a hygroscopic material,which leads to the gradual occurrence of humidity in the briquettes.This causes a reduction in the strength of the briquette and in itsstorage period and length of life. The briquettes gradually lose theirstrength, and after a certain time become unusable.

For example, in the case of briquettes of cylindrical shape with aweight of 100-150 g, this time period is 5 to 7 months. In a certainfashion, the length of life of the briquettes may be prolonged bywrapping in polyethylene, and by storage in areas with low relativehumidity.

Using the method described, briquettes are obtained from the briquettingmixture with a content by weight of over 95% slag from secondaryaluminium processing, up to 5% polyvinyl acetate polymer, the best up to1.5%, and of residue humidity a maximum of 1.5% water, best no more than0.5% water, in relation to the overall mass of the briquette, with aspecific weight of 1,500 to 5,000 kg.m⁻³, best around 2,000 kg.m⁻³, andwith a compression strength of at least 20 MPa and ideally around 100MPa.

The quality of the final product depends not only on the basic rawmaterials, especially the composition and properties of the slag, thecontent of polyvinyl acetate dispersion, hydrophobic ingredient, ifused, and water, but also on the manner in which this slag is processed,which also affects the specific weight and compression strength of thevarious shapes of briquette.

In its optimum composition, the briquetting mixture contains, by weight:

92% slag from secondary aluminium processing,

1% polyvinyl acetate dispersion, and

7% water.

From this composition of briquetting mixture, the process describedenables briquettes to be produced with the optimum shape properties,i.e. a cylinder of diameter 35-50 mm at a height of 15-50 mm, a weightof around 120 g and a specific weight of around 2,000 kg.m⁻³, with acompression strength against decomposition of around 100 MPa, a residuewater content of maximally 0.5% and resistance to decomposition, afterpackaging, for 7 months and more.

Other possible versions of briquetting mixtures and briquettes withresistance to decomposition of 7 months and more are described below.

EXAMPLE 2

The briquetting mixture contains, by weight:

91% slag from secondary aluminium processing,

2% polyvinyl acetate dispersion, and

7% water.

Briquettes produced by the method described have a compression strengthof 95 MPa, a water content of 0.6% by weight in relation to the overallweight of the briquette, and a specific weight of 2,000 kg.m⁻³.

EXAMPLE 3

The briquetting mixture contains:

90% slag from secondary aluminium processing,

3% polyvinyl acetate dispersion, and

7% water.

Briquettes produced by the method described have a compression strengthof 95 MPa, a water content of 0.4% by weight in relation to the overallweight of the briquette, and a specific weight of 2,100 kg.m⁻³.

EXAMPLE 4

The briquetting mixture contains:

91.5% slag from secondary aluminium processing,

1% polyvinyl acetate dispersion,

0.5% hydrophobic ingredient in the form of oleic acid, and

7.0% water.

Briquettes produced by the method described have a compression strengthof around 85 MPa, a water content of 0.5% by weight in relation to theoverall weight of the briquette, and a specific weight of 2,100 kg.m⁻³.

EXAMPLE 5

The briquetting mixture contains:

91% slag from secondary aluminium processing,

1% polyvinyl acetate dispersion,

1% hydrophobic ingredient in the form of oleic and/or stearic acid, and

7% water.

Briquettes produced by the method described have a compression strengthof around 90 MPa, a water content of 0.5% in relation to the overallweight of the briquette, and a specific weight of 2,000 kg.m⁻³.

EXAMPLE 6

The briquetting mixture contains:

87.5% slag from secondary aluminium processing,

8.0% polyvinyl acetate dispersion,

0.5% hydrophobic ingredient in the form of oleic and/or palmiticacid,and

4% water.

Briquettes produced by the method described have a compression strengthof approx. 110 MPa, a water content of 0.5% in relation to the overallweight of the briquette, and a specific weight of 2,300 kg.m⁻³.

EXAMPLE 7

The briquetting mixture contains:

95% slag from secondary aluminium processing,

2% polyvinyl acetate dispersion,

0.2% hydrophobic ingredient in the form of oleic acid, and

2.8% water.

Briquettes produced by the method described have a compression strengthof around 100 MPa, a water content of 0.5% in relation to the overallweight of the briquette, and a specific weight of 2,300 kg.m⁻³.

These examples of versions do not exclude other possible combinationsand variations within the scope of the intention of the patent claims.

INDUSTRIAL APPLICABILITY

Besides the liquefaction of metallurgical slag, the briquettes are alsosuitable for the preparation of raw materials for cement manufacture,for the treatment of waste products destined for storage on dumpinggrounds, and for the bonding of graphite, carbonaceous and othermaterials.

The briquettes obtained by this technological method are intended mainlyfor the dilution of slags in slag runners, for the treatment of thealuminate module for slag used in cement manufacture, for the creationof synthetic slags for copper metallurgy, for the dilution of slags inarc furnaces, as a substitute for fluorite, limestone, bauxite, quartzsands etc. During usage, the briquettes also have slight desulphurisingand dephosphorising properties.

What is claimed is:
 1. Briquettes for the liquefaction of metallurgicalslag, formed from a mixture comprising, by weight, 85-98% slag fromsecondary aluminium processing, 1-8% polyvinyl acetate dispersion as apolymeric bonding agent, and remainder of water; the briquettescontaining water in the form of residue humidity in a quantity of up to1.5% by weight in relation to the overall weight of the briquettes,wherein the briquettes have has a specific weight of 1,500-5,000 kg.m⁻³and a compression strength of at least 20 MPa.
 2. Briquettes accordingto claim 1, containing residue humidity in an amount of up to 0.5% byweight in relation to the overall weight of the briquettes. 3.Briquettes according to claim 1, wherein the mixture contains, byweight, 90-92% slag from secondary aluminium processing, 1-3% polyvinylacetate dispersion and remainder of water.
 4. Briquettes according toclaim 1, wherein the mixture also contains, by weight, 0.5-2%unsaturated acid, selected from the group consisting of oleic acid,palmitic acid and stearic acid, as a hydrophobic ingredient. 5.Briquettes according to claim 1, wherein said briquettes are cylindricalin shape.
 6. Method of manufacture of briquettes according to claim 1,comprising the steps of mixing slag from secondary aluminium processing,polyvinyl acetate dispersion as bonding agent and water for a period of10-60 seconds to form a homogenous mixture; pressing the homogenousmixture at a specific press power of 110 to 130 MPa to form briquettes;drying the briquettes at a temperature between 120 and 200° C. for aperiod of 30-60 minutes, depending on the weight of the briquettes,until the amount of residue water is reduced to a maximum value of 1.5%by weight, and after drying, cooling the hot briquettes, and wrappingthe cooled briquettes for protection against humidification.
 7. Methodaccording to claim 6, including a step of preheating the mixture to atemperature of 25 to 90° C. prior to mixing the components into ahomogenous state in the mixer.
 8. Method according to claim 6, whereinafter drying and prior to wrapping, cooling the hot briquettes to 30-50°C.